#include <iostream>
#include "Sales_item.h"

int main ()
{
	Sales_item item1,item2;
	std::cout<< "pllease enter two numbers:";
	std::cin>> item1>> item2;
	if (item1.isbn() == item2.isbn()){
		std::cout<< item1 + item2<< std::endl;
		return 0;
	}
	else {
		std::cerr<<"Data must refer to same isbn "<< std::endl;
		return -1;

	}
}